PC Labs Preamp Setup

Each PC lab except for the large 6 person group PC Lab (Group Lab 4) should be equipped with a neckworn cardiod (directional) microphone and a tube preamplifier to ensure quality recordings. However to function correctly the preamp needs to be configured correctly for each subject.

Preamp starting position

Before starting the setup checklist ensure that the preamp is in the following state (Fig 1).

• Input knob turned fully to the left
• Output know turned fully to the left
• +20dB gain buttion (down)
• P-Pwr +48V (down)
• Phase reverse (up)
• Power/Clip LED should be bright green

Fig 1. ART TubeMP Preamplifier in the starting position.

Setting input and output gains

1. Open the program "Audacity" and click the record button.
2. Start counting from 1 to infinity whilst turning the input knob to the right. When the Power/Clip LED starts showing some red turn the knob a little bit back to the left until the LED stays a constant green.
3. Keep counting and now turn the output knob to the right whilst observing the recording in Audacity. You should now see the waveforms being recorded as you count. Keep turning the knob until the waveforms are as large as possible without extending past the top and bottom borders of the recording window. An example is provided below (Fig 2), the first few waveforms here have to much output gain, the last few are about right.
4. Click the stop button in Audacity and stop counting :)
5. Play back this recording to check your setup.
6. Close Audacity, there is no need to save this recording.

Fig 2. Setting output gains levels from the preamp using Audacity.

Turning off the microphone

When you've finished testing the preamp should be set to the following position. This will turn off the microphone and improve its longevity, the preamp however will remain on, this is fine.

• Input knob turned fully to the left
• Output knob turned fully to the left
• +20dB gain buttion (up)
• P-Pwr +48V (up)
• Phase reverse (up)
• Power/Clip LED should be bright green